Soil conditioner, preparation method and application

Abstract

The invention belongs to the technical field of agricultural soil conditioners, and particularly relates to a soil conditioner, a preparation method and application. The invention provides a soil conditioner. The soil conditioner comprises fermented sludge, modified bentonite and lignosulfonate, the mass ratio of the fermented sludge to the modified bentonite to the lignosulfonate is (6-8): (2-3): (1-3). When the soil conditioner is applied to saline alkali soil, the pH value of the soil can be reduced, the organic matter content of the soil can be increased, the microbial diversity index (Shannon index) of the soil can be increased, and heavy metal in the soil can be passivated; meanwhile, the soil conductivity value is reduced. Compared with a traditional lime improvement method, the soil conditioner can avoid the risk of secondary alkalization and is good in application effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural soil conditioners, and particularly relates to a soil conditioner, a preparation method and an application thereof. Background Art

[0002] Sludge is a solid waste. For example, municipal sludge is a solid waste generated in the process of urban sewage treatment, containing a large amount of organic matter and nutrient elements, but at the same time may also contain harmful substances such as heavy metals and pathogenic microorganisms. Traditional sludge treatment methods (such as landfilling, incineration) not only waste resources, but also may cause secondary pollution to the environment.

[0003] At present, soil improvement generally adopts the chemical method. For example, in alkaline soil, alkalized soil, and soda saline soil, modifiers such as gypsum and ferrous sulfate are applied to reduce or eliminate soil alkalinity and improve the physical and chemical properties of the soil. However, there is a risk of secondary alkalization, and the effect of improving soil organic matter is limited. Therefore, it is very necessary to develop an efficient and environmentally friendly soil conditioner. Summary of the Invention

[0004] The present invention provides a soil conditioner, a preparation method and an application thereof. The soil conditioner of the present invention can avoid the risk of secondary alkalization, and can simultaneously increase the content of soil organic matter, the soil microbial diversity index, reduce the soil pH and passivate heavy metals.

[0005] In order to solve the above technical problems, the following technical solutions are proposed: The present invention provides a soil conditioner, comprising fermented sludge, modified bentonite and lignosulfonate; the mass ratio of the fermented sludge, modified bentonite and lignosulfonate is (6-8):(2-3):(1-3); The preparation of the fermented sludge includes: fermenting the sludge with a composite bacterium agent to obtain fermented sludge; the composite bacterium agent includes Bacillus stearothermophilus ( Bacillus stearothermophilus ), Aspergillus niger ( ‌Aspergillus niger ‌), and Trichoderma reesei ( Trichodermareesei ); The modified bentonite includes citric acid modified bentonite.

[0006] Preferably, the application forms of the Bacillus stearothermophilus, Aspergillus niger and Trichoderma reesei include bacterium agents, and the mass ratio of the Bacillus stearothermophilus bacterium agent, Aspergillus niger bacterium agent and Trichoderma reesei bacterium agent is (2-4):(1-2):(2-3).

[0007] Preferably, the fermentation includes aerobic fermentation and anaerobic fermentation in sequence; the temperature of the aerobic fermentation is 50-60°C, and the time is 4-8d; the temperature of the anaerobic fermentation is 30-50°C, and the time is 10-20d.

[0008] Preferably, the addition amount of the compound bacterium agent is 1% - 3% of the dry weight of the sludge.

[0009] Preferably, the preparation of the citric acid-modified bentonite includes: mixing the bentonite and the citric acid solution for modification; the mass-volume ratio of the bentonite to the citric acid solution is 1 g : (7 - 9) mL; the temperature of the modification is 50 - 90 °C, and the time is 2 - 8 h.

[0010] The present invention provides a preparation method of the soil conditioner described in the above technical solution, including: mixing the fermented sludge, the modified bentonite and the lignosulfonate, and then performing microwave crosslinking to obtain the soil conditioner.

[0011] Preferably, the power of the microwave crosslinking is 700 - 1000 W, and the irradiation time of the microwave crosslinking is 3 - 5 min.

[0012] The present invention provides an application of the soil conditioner described in the above technical solution or the soil conditioner prepared by the preparation method described in the above technical solution in soil improvement.

[0013] Preferably, the soil includes saline-alkali soil.

[0014] Preferably, the soil improvement includes at least one of the following: 1) Reducing the soil pH value; 2) Passivating soil heavy metals; 3) Reducing the soil conductivity value; 4) Increasing the soil microbial diversity index; 5) Increasing the soil organic matter content.

[0015] The beneficial effects of the present invention: The present invention provides a soil conditioner, including fermented sludge, modified bentonite and lignosulfonate; the mass ratio of the fermented sludge, the modified bentonite and the lignosulfonate is 7:2:1; the preparation of the fermented sludge includes: fermenting the sludge with a compound bacterium agent to obtain fermented sludge; the compound bacterium agent includes Bacillus stearothermophilus ( Bacillus stearothermophilus ), Aspergillus niger ( ‌Aspergillus niger ‌), and Trichoderma reesei ( Trichodermareesei ); The modified bentonite includes citric acid-modified bentonite.

[0016] The present invention mixes the sludge and the compound bacterium agent and then ferments them to obtain fermented sludge; the compound bacterium agent includes Bacillus stearothermophilus, Aspergillus niger and Trichoderma reesei; mixes the bentonite and the citric acid solution and then performs modification to obtain modified bentonite.

[0017] The present invention conducts directional fermentation on sludge, synthesizes humic acid substances through microbial metabolism, has a high organic matter content, and the humic acid synthesized during the fermentation stage contains abundant carboxyl / phenolic hydroxyl functional groups, significantly enhancing the replacement ability for Na + in saline-alkali soil and reducing the pH value of the soil. Additionally, bentonite forms a porous carrier structure after being activated by citric acid, has a high specific surface area, can load the active organic matter in the fermentation product and delay nutrient release, and increases the organic matter content of the soil; the pore structure of the modified bentonite is more abundant and the adsorption rate is higher, and it can adsorb more salt-causing ions such as chloride ions, and combined with its slow-release characteristics, the EC value of the soil decreases steadily. Additionally, lignosulfonate forms a stable complex with heavy metals through π-π interaction, synchronously achieving the passivation of heavy metals in the soil. Under the synergistic effect of fermented sludge, modified bentonite and lignosulfonate, soil improvement is realized, the organic matter content of the soil, the soil microbial diversity index are increased, the soil pH is reduced, and heavy metals are passivated. Brief Description of the Drawings

[0018] 图1 It is a scanning electron microscope (SEM) image of the soil conditioner; 图2 It is a process flow chart for the preparation of the soil conditioner. Detailed Embodiments

[0019] The present invention provides a soil conditioner, comprising fermented sludge, modified bentonite and lignosulfonate; the mass ratio of the fermented sludge, modified bentonite and lignosulfonate is (6-8):(2-3):(1-3), more preferably 7:2:1.

[0020] The preparation of the fermented sludge in the present invention includes: fermenting sludge with a composite bacterial agent to obtain fermented sludge; the composite bacterial agent includes Bacillus stearothermophilus ( Bacillus stearothermophilus ), Aspergillus niger ( ‌Aspergillus niger ‌), and Trichoderma reesei ( Trichodermareesei ); The modified bentonite includes citric acid-modified bentonite.

[0021] As an alternative embodiment, the application forms of the Bacillus stearothermophilus, Aspergillus niger, and Trichoderma reesei in the present invention include microbial agents; the preparation method of the composite microbial agent in the present invention includes: mixing the Bacillus stearothermophilus microbial agent, Aspergillus niger microbial agent, and Trichoderma reesei microbial agent; the mass ratio of the Bacillus stearothermophilus microbial agent, Aspergillus niger microbial agent, and Trichoderma reesei microbial agent during mixing is (2-4):(1-2):(2-3), or can also be (2.5-4):(1-2):(2-2.5), preferably 3:1:2; the present invention has no special limitations on the parameters of the mixing, and conventional methods can be used. The present invention has no special limitations on the sources of the Bacillus stearothermophilus, Aspergillus niger, and Trichoderma reesei, and conventional strains can be used. The Bacillus stearothermophilus in the present invention is the "main bacterium" for the decomposition of organic matter at the high-temperature stage, and can also significantly improve the humic acid synthesis efficiency through mechanisms such as enzymatic degradation, precursor supply, and microbial synergy, and enhance the functionality of soil conditioners such as high-temperature adaptability, pollutant degradation ability, and stress resistance, providing key technical support for the resource utilization of municipal sludge and the remediation of saline-alkali land. Aspergillus niger is not only the "core decomposer" of cellulose / lignin decomposition, but also directly drives the efficient synthesis of humic acid through acid production regulation, polyphenol precursor supply, and the generation of reducing substances. Its synergistic effect with Bacillus stearothermophilus and cellulose-decomposing bacteria realizes the utilization of all components of organic matter and the deep degradation of pollutants, providing a biochemical basis for the functionality of the conditioner (such as Na + replacement, heavy metal passivation). In addition, the biosorption characteristics of Aspergillus niger further ensure the biosafety of the soil conditioner, making it both efficient and environmentally friendly in the remediation of saline-alkali land. Trichoderma reesei can secrete cellulase to decompose cellulose; under the combined action of Bacillus stearothermophilus, Aspergillus niger, and Trichoderma reesei, the humic acid production rate of fermented sludge is increased. In the examples of the present invention, the Bacillus stearothermophilus is purchased from the American Type Culture Collection, and the preservation number is ATCC12980; the preservation number of Aspergillus niger is CMCC 98003; the Trichoderma reesei ( Trichodermareesei is purchased from the American Type Culture Collection, and the preservation number is ATCC 26921.

[0022] As an alternative embodiment, a composite microbial agent is obtained, and the composite microbial agent is used in the present invention to ferment the pretreated sludge to obtain fermented sludge. The preparation method of the pretreated sludge in the present invention includes: centrifugally dehydrating, drying, and pulverizing the sludge to obtain the pretreated sludge. As an alternative embodiment, the sludge includes municipal sludge. In a specific embodiment of the present invention, the municipal sludge is the sludge provided by the Xiaojiahe Reclaimed Water Plant. The present invention has no special limitation on the parameters of the centrifugal dehydration, and a conventional method can be used. The temperature of the drying is 85°C, and it is dried until the water content ≤ 10%; it is pulverized to a particle size of 80 mesh. The pretreated municipal sludge is conducive to resource utilization. The core value of the pretreated sludge lies in transforming "waste" into "urban mines". When specifically selecting the application direction, it is necessary to combine the sludge characteristics, technical feasibility, and market demand, and give priority to developing technical paths with high added value and low environmental risks to promote the development of circular economy. As an alternative embodiment, the addition amount of the composite microbial agent during fermentation is 1% - 3% of the dry weight of the sludge, and more preferably 2%.

[0023] As an alternative embodiment, the fermentation includes aerobic fermentation and anaerobic fermentation carried out in sequence. In the present invention, the temperature of the aerobic fermentation is 50 - 60°C, or can also be 52 - 58°C, preferably 55°C, and the time is 4 - 8 d, or can also be 4.5 - 7 d, preferably 5 d; the aerobic fermentation promotes the rapid decomposition of organic matter. The temperature of the anaerobic fermentation is 30 - 50°C, or can also be 38 - 47°C, preferably 45°C, and the time is 10 - 20 d, or can also be 12 - 18 d, preferably 15 d. The anaerobic fermentation synthesizes humic acid-like substances through microbial metabolism. The settings of the temperature and time parameters of the aerobic fermentation and anaerobic fermentation in the present invention can increase the humic acid production rate and degrade stubborn pollutants such as polycyclic aromatic hydrocarbons; and the humic acid synthesized in the fermentation stage contains rich carboxyl / phenolic hydroxyl functional groups, significantly enhancing the replacement ability of Na + in saline-alkali soil, and the humic acid content in the fermented sludge is high.

[0024] As an alternative embodiment, bentonite and a citric acid solution are mixed in the present invention for modification to obtain citric acid-modified bentonite. As an alternative embodiment, the mass concentration of the citric acid solution is 2% - 5%, or can also be 2.5% - 4%, preferably 3%. As an alternative embodiment, the mass-volume ratio of the bentonite and the citric acid solution in the present invention is 1 g : (7 - 9) mL, and more preferably 1 g : 8 mL. As an alternative embodiment, the temperature of the modification in the present invention is 50 - 90°C, or can also be 55 - 70°C, more preferably 60°C; the time is 2 - 8 h, or can also be 2 - 5 h, more preferably 2 h. After the bentonite is activated by the citric acid solution with a certain mass concentration, a porous carrier structure is formed, and the specific surface area is increased to 210 m 2 / g, it can carry more active organic matter in the fermentation products and delay the nutrient release, thus increasing the organic matter content of the soil. The pore structure of the modified bentonite is more abundant, which can adsorb salt-causing ions such as chloride ions, and the adsorption rate is higher. Combining with its slow-release characteristics, the soil EC value steadily decreases within 60 days.

[0025] The soil conditioner of the present invention further includes lignosulfonate, and the lignosulfonate forms stable complexes with heavy metals Pb 2+ , Cd 2+ to reduce the heavy metal content in the soil. Among them, the binding constants of lignosulfonate with Pb 2+ , Cd 2+ reach 10 8.3 and 10 7.1 respectively, synchronously achieving the passivation of heavy metals in the soil.

[0026] The mass ratio of the fermented sludge, modified bentonite and lignosulfonate in the soil conditioner of the present invention is (6 - 8):(2 - 3):(1 - 3), preferably 7:2:1. In the present invention, there is a synergistic effect among the fermented sludge, modified bentonite and lignosulfonate in the soil conditioner, which can stably reduce the pH value and EC value of the soil, achieve the passivation of heavy metals in the soil, increase the organic matter content of the soil and improve the soil microbial diversity index. As an optional implementation manner, the lignosulfonate preferably includes sodium lignosulfonate.

[0027] The present invention provides a preparation method of the soil conditioner described in the above technical solution, including: mixing the fermented sludge, modified bentonite and lignosulfonate, and then performing microwave crosslinking to obtain the soil conditioner. The present invention has no special limitation on the parameters of the mixing, and conventional methods can be used. As an optional implementation manner, the power of the microwave crosslinking is 700 - 1000 W, preferably 800 W, and the irradiation time of the microwave crosslinking is 3 - 5 min, preferably 3 - 4 min. After the microwave crosslinking treatment, the material forms a granular conditioner with a microcapsule structure. The soil conditioner of the present invention is a granular conditioner with a particle size range of 1 - 3 mm. By compounding the fermentation product with modified bentonite and lignosulfonate in a specific ratio and combining with microwave-assisted crosslinking technology, the binding stability among the fermented sludge, modified bentonite and lignosulfonate is enhanced, forming a granular conditioner with a microcapsule structure, significantly improving the stability and slow-release performance of the soil conditioner. The porous carrier structure of the modified bentonite and the heavy metal passivation ability of the lignosulfonate synergistically enhance the repair effect of the conditioner on saline-alkali soil.

[0028] The present invention provides the application of the soil conditioner in soil improvement described in the above technical solution. As an alternative embodiment, the soil includes saline-alkali soil. As an alternative embodiment, the soil improvement of the present invention includes at least one of the following: 1) reducing the soil pH value; 2) passivating soil heavy metals; 3) reducing the soil EC value; 4) increasing the soil microbial diversity index; 5) increasing the soil organic matter content.

[0029] As an alternative embodiment, the application rate of the soil conditioner of the present invention is 2 - 3 t / ha. The soil conditioner of the present invention is applied to saline-alkali soil for 7 - 50 days, which can also be 14 - 47 days, and more preferably 45 days. The soil conditioner can reduce the soil pH value, increase the soil organic matter content, increase the soil microbial diversity index (Shannon index), passivate heavy metals, and reduce the soil EC value. After the soil conditioner of the present invention improves the soil, it improves the oxygen and moisture conditions of the soil, provides a suitable living space for microorganisms, and increases the soil microbial diversity index.

[0030] Compared with the traditional lime improvement method, the soil conditioner of the present invention avoids the risk of secondary alkalization.

[0031] Traditional sludge treatment methods (such as landfilling and incineration) not only waste resources but also may cause secondary pollution to the environment, while the present invention provides a new environmentally friendly and economical sludge treatment approach. The present invention uses sludge as a raw material and converts it into an efficient humified soil conditioner through directional fermentation and functional compounding technologies, realizing the efficient resource utilization of municipal sludge. Saline-alkali soil seriously restricts agricultural production and ecological restoration due to its high salt content, low organic matter, and poor microbial community. The present invention combines the resource utilization of municipal sludge with the restoration of saline-alkali land and develops an efficient and environmentally friendly soil conditioner through the directional fermentation, functional compounding, and synergistic action mechanism of composite bacterial agents, which has significant environmental and economic benefits. The soil conditioner of the present invention is weakly acidic and can avoid the risk of secondary alkalization.

[0032] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to examples, but they cannot be understood as limiting the protection scope of the present invention.

[0033] Bacillus stearothermophilus ( Bacillus stearothermophilus ) bacterial agent: purchased from the American Type Culture Collection, and the preservation number of Bacillus stearothermophilus is ATCC 12980; the viable count of the purchased Bacillus stearothermophilus bacterial agent is 10 8 ~10 9 CFU / g.

[0034] Aspergillus niger ( ‌Aspergillus niger ‌) Bacterial agents: Purchased from the China Medical Bacteria Preservation Management Center (CMCC), the preservation number of Aspergillus niger is CMCC 98003; the viable count of the bacterial agent is 10 6 ~10 7 CFU / g.

[0035] Trichoderma reesei ( Trichodermareesei ) Bacterial agent: Purchased from the American Type Culture Collection (ATCC), the preservation number is ATCC 26921; Trichoderma reesei secretes cellulase; the viable count of the bacterial agent is 10 7 ~10 8 CFU / g.

[0036] Preparation of fermented sludge in Example 1 1. Take 100 kg of municipal sludge. After centrifugal dehydration, the moisture content of the sludge is reduced from 80% to 60%. The dehydrated sludge is dried at 85 °C until the moisture content ≤ 10%. Weigh it to obtain the dry weight of the sludge; the dried sludge is crushed to a particle size of 80 mesh to obtain dry sludge powder.

[0037] 2. Prepare a composite bacterial agent by mixing the bacterial agents of Bacillus stearothermophilus, Aspergillus niger and Trichoderma reesei according to a mass ratio of 3:1:2 to obtain a composite bacterial agent.

[0038] 3. Inoculate the composite bacterial agent into the dry sludge powder at 2% of the dry weight of the sludge and mix well. The inoculated sludge is placed in an aerobic fermentation tank, and the temperature is controlled at 55 °C for 5 days of fermentation. During the fermentation process, stir regularly to ensure oxygen supply and promote the rapid decomposition of organic matter. Transfer the material after aerobic fermentation to an anaerobic fermentation tank, control the temperature at 45 °C, and ferment for 15 days to obtain fermented sludge (i.e., the fermentation product). During anaerobic fermentation, microorganisms metabolize and synthesize humic acid-like substances and degrade refractory pollutants such as polycyclic aromatic hydrocarbons. After fermentation, the humic acid formation rate is measured to be 45%.

[0039] The replacement ability of humic acid in the fermented sludge for Na + in saline-alkali soil is significantly enhanced, and the Na + removal rate measured by atomic absorption spectrometry reaches 75%.

[0040] The steps for measuring by atomic absorption spectrometry are as follows: Control group: Take 10 g of a certain amount of municipal sludge and add 50 mL of deionized water as the extractant, shake (200 rpm, 25 °C) for 1 h, centrifuge (4000 rpm, 10 min), and take the supernatant and filter for standby.

[0041] Experimental group: Mix 10 g of the same mass of fermented sludge with 50 mL of humic acid solution, shake under the same conditions, and the subsequent steps are the same as those of the control group.

[0042] Instrument parameter settings for atomic absorption spectrometry: Wavelength: 589.0 nm (sodium characteristic spectral line); the lamp current and slit width are optimized according to the instrument instruction manual of the Higuang HGA-E50 flame graphite furnace integrated atomic absorption spectrophotometer.

[0043] Standard curve plotting Measure the absorbance of the sodium standard solution and plot the concentration-absorbance standard curve (R 2 should be ≥ 0.995).

[0044] Sample determination Measure the absorbance of the leachate of the control group and the treatment group respectively, and calculate the Na⁺ concentration through the standard curve.

[0045] Comparative example 1: Traditional single-bacteria agent fermentation Traditional single-bacteria agent fermentation method of Bacillus subtilis ( Bacillus subtilis ): Source of bacteria: Standard bacteria library (CMCC 63501) Storage condition: Glycerol tube (-80°C).

[0046] Formulation of activation medium: Peptone 10 g / L, beef extract 5 g / L, and NaCl 5 g / L, pH 7.0 - 7.2. Steps: Take 1 loop of Bacillus subtilis bacteria and inoculate it into the liquid activation medium, and culture it with shaking at 30°C and 180 rpm for 12 - 16 h (until OD 600 ≈ 1.0) to obtain the seed liquid. Transfer the seed liquid to a new activation medium according to the inoculation amount of 5% of the medium volume ratio, and culture it with shaking at 30°C and 180 rpm until the logarithmic growth phase (OD 600 ≈ 2.0) to obtain the bacterial liquid.

[0047] After drying, the sludge is sieved through a 40-mesh sieve to increase the specific surface area, soaked in a 2% NaOH solution with a mass concentration for 24 h. During soaking, the solid-liquid ratio of the dried sludge to the NaOH solution is 1 g:10 mL. After soaking, the obtained product is washed with water until neutral to remove the lignin barrier, and then autoclaved at 21°C for 20 min.

[0048] After sterilization, the bacterial liquid is added to the sludge and fermented aerobically at a constant temperature of 30°C. The aerobic fermentation is stirred at 200 rpm, and the ventilation volume is 1 vvm to maintain the dissolved oxygen ≥ 30% saturation. The fermentation time is 72 h.

[0049] After the fermentation in comparative example 1 is completed, the humic acid production rate is measured to be 32%.

[0050] After the fermentation in Example 1 is completed, the humic acid production rate is measured to be 45%, which is 40.6% higher than that in comparative example 1.

[0051] The degradation rate of polycyclic aromatic hydrocarbons was determined by SPME-GC / MS (solid phase microextraction-gas chromatography / mass spectrometry). The degradation rate of polycyclic aromatic hydrocarbons (PAHs) in the sludge of Example 1 reached over 85%.

[0052] The degradation rate of polycyclic aromatic hydrocarbons was determined by SPME-GC / MS (solid phase microextraction-gas chromatography / mass spectrometry). The specific determination process is as follows: Weigh 10 g of dry fermented sludge, add 3:5 (mL / g) deionized water, perform ultrasonic-assisted extraction for 30 min, and centrifuge to obtain the supernatant. Remove impurities through a solid-phase extraction column. The supernatant is concentrated to 0.5 mL by nitrogen blowing, filtered through a 0.22 μm filter membrane, and the filtrate is reserved for use.

[0053] Select the coating fiber for the extraction fiber: The coating fiber is 65 µm polydimethylsiloxane / divinylbenzene (PDMS / DVB) (suitable for trace PAHs, with an adsorption efficiency higher than 100 µm PDMS). Pretreatment: The coating fiber needs to be aged at 300 °C for 1 hour before the first use to remove impurities.

[0054] Perform extraction on the filtrate. The extraction parameters are as follows: Temperature: 40 °C (too high will cause loss of volatile PAHs). Time: 40 min for water body sample extraction, 20 min for headspace sample. Stirring speed: 350 - 500 rpm to enhance mass transfer efficiency.

[0055] Preparation of the soil conditioner in Example 2 Take 100 kg of bentonite, add a citric acid solution with a mass concentration of 3%, with a mass ratio of 1 g:8 mL, then stir and activate at 60 °C for 2 h, and then filter, wash, and dry to obtain citric acid-modified bentonite, with the specific surface area increased to 210 m 2 / g.

[0056] Take 700 kg of the fermentation product of Example 1, 200 kg of citric acid-modified bentonite, and 100 kg of sodium lignosulfonate, and mix them in a mass ratio of 7:2:1. Place the compound mixture in a microwave reactor, set the power to 800 W, and irradiate for 3 min. After microwave treatment, the material forms a granular conditioner with a microcapsule structure, that is, a granular soil conditioner.

[0057] The specific mechanism for the preparation of the soil conditioner is as follows: Step 1: Premixing of components and physical adsorption.

[0058] Dry-mix the fermented sludge (ground to 80 mesh), citric acid-modified bentonite, and lignosulfonate in a mass ratio of 7:2:1. The porous structure of bentonite adsorbs the organic matter of the fermented sludge through capillary action to form a preliminary composite particle.

[0059] Step 2: Microwave-assisted crosslinking (core process) Microwave action mechanism.

[0060] Microwave (800W, 3min) induces local high temperature (80~100°C), which promotes the enhanced movement of lignosulfonate molecular chains and exposes more active groups (-SO3H, -OH); the non-thermal effect of microwave (polar molecular directional vibration) accelerates the formation of hydrogen bonds and coordination bonds.

[0061] Crosslinking reaction: Bentonite-lignosulfonate: Al between bentonite layers 3+ Combines with -SO3H of lignosulfonate through ionic bonds.

[0062] Fermented sludge and bentonite crosslinking: The carboxyl group (-COOH) of humic acid forms hydrogen bonds with -OH on the bentonite surface; Fermented sludge and lignosulfonate crosslinking: The quinone group (C=O) of humic acid crosslinks with the benzene ring of lignosulfonate through π-π stacking.

[0063] Step 3: Microcapsule structure shaping During the cooling process of the crosslinked composite, the layered structure of bentonite shrinks to wrap the fermented sludge particles, and lignosulfonate acts as a "glue" to fill the pores, finally forming a core-shell microcapsule structure with fermented sludge as the core and bentonite-lignosulfonate as the shell layer (particle size about 0.5~2mm), that is, forming a granular soil conditioner with a microcapsule structure.

[0064] It is measured that the particle size range of the granular soil conditioner is 1~3mm, and it has good slow-release characteristics. By observing the soil conditioner through scanning electron microscopy (SEM), the particle surface presents a porous structure, and the active organic matter is evenly loaded, see 图1 . The preparation process of the soil conditioner is shown in 图2 .

[0065] Example 3 pH of saline-alkali soil sample: 9.2; Electrical conductivity: 5.5 dS / m; Bulk density is 1.6 g / cm 3 ; Cation exchange capacity: 15 cmol(+) / kg.

[0066] Take the saline-alkali soil sample, air-dry it and pass it through a 2 mm sieve, and apply the granular conditioner obtained in Example 2 to the saline-alkali soil at a application rate of 2.5 t / ha. Temperature: 25~30°C (simulating the field environment). Humidity: Keep the soil water content at 60%~70% (maximum water holding capacity). Cultivation period: 45 days, turn the soil once every 5 days to promote the reaction. After the cultivation, rotary till and bury it to a depth of 20 cm.

[0067] The soil pH value decreased from 8.9±0.3 to 7.2±0.1. The soil organic matter content increased from 1.2% to 2.8%. Through ultraviolet-visible spectroscopy (UV-Vis) analysis, the binding constants of lignosulfonate with Pb 2+ and Cd 2+ reached 10 8.3 and 10 7.1 , respectively. The activity of heavy metals Pb 2+ and Cd 2+ in the soil decreased by more than 90%, achieving heavy metal passivation. Through ion chromatography analysis, the adsorption capacity of modified bentonite for Cl - was 120 mg / g. The soil EC value decreased from 4.5 mS / cm to 2.3 mS / cm within 60 days, with a decrease of 49%.

[0068] The soil microbial diversity index (Shannon index) increased from 2.1 to 5.7, a 1.7-fold increase. Compared with the traditional lime improvement method, this method avoids the risk of secondary alkalization.

[0069] Example 4 Experimental group: Parameters of the sample soil: The sample soil was from the soda saline-alkali land in Daan, Jilin. Soil pH value: 9.3; Electrical conductivity: 13 mS / cm; Initial exchangeable sodium percentage (ESP): 40%; Organic matter content: 1.2%.

[0070] The granular soil conditioner prepared by the method of Example 2 of this example was used. The sample soil and the soil conditioner were mixed at a mass ratio of 5:1. After mixing, the temperature was 25 - 30 °C (simulating the field environment). Humidity: Keep the soil water content at 60% - 70% (maximum water holding capacity) for cultivation. The cultivation period was 45 days, and the soil was turned over every 5 days to promote the reaction. After the cultivation, the soil was measured.

[0071] Control group: The soil treated by the traditional lime improvement method, specifically: Take the soda saline-alkali land soil in Daan, Jilin (initial ESP = 40%, pH = 9.3), add CaCO3 powder accounting for 3% of the mass of the soda saline-alkali land soil. After adding, mix well (mechanical stirring or manual mixing) to ensure uniform contact to obtain a mixture. After mixing, the temperature was 25 - 30 °C (simulating the field environment). Humidity: Keep the soil water content at 60% - 70% (maximum water holding capacity) for cultivation. The cultivation period was 45 days, and the soil was turned over every 5 days to promote the reaction.

[0072] The same batch of soda saline-alkali land soil in Daan, Jilin was used in the control group and the experimental group. The specific measurement methods for the control group and the experimental group are as follows: (1) Measure the organic matter content of the treated soil by the potassium dichromate oxidation method.

[0073] (2) The pH of the treated soil was measured using a pH meter (FE20, Mettler Toledo, Shanghai).

[0074] (3) The EC value was measured using a Hanna HI983302N suspended conductivity EC continuous measurement instrument.

[0075] (4) The method for determining the heavy metal passivation effect was the BCR sequential extraction method.

[0076] The measurement results of the soil obtained from the control group and the experimental group are as follows: (1) The pH value of the soil in the experimental group was stable at 7.2 ± 0.1, while the pH value of the soil in the control group fluctuated greatly (8.5 - 9.0).

[0077] (2) The organic matter content of the soil in the experimental group increased to 2.8%, while that in the control group was only 1.5%.

[0078] (3) The EC value of the soil in the experimental group was 6.76 mS / cm, and that in the control group was 10.4 mS / cm. Compared with the control group, the soil EC value of the experimental group decreased by 35%.

[0079] (4) The heavy metal passivation effect of the experimental group was significantly better than that of the control group. The CdCO3 precipitation in the control group was 0.37 mg / kg, and that in the experimental group was 0.44 mg / kg, an increase of 18.9%.

[0080] In summary, when the soil conditioner of the present invention is applied to saline-alkali soil, it can reduce the soil pH value, increase the soil organic matter content, and increase the soil microbial diversity index (Shannon index). Compared with the traditional lime improvement method, the soil conditioner of the present invention avoids the risk of secondary alkalization.

[0081] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all embodiments. People can also obtain other embodiments based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A soil conditioner, characterized in that, It includes fermented sludge, modified bentonite and lignosulfonate; the mass ratio of the fermented sludge, modified bentonite and lignosulfonate is (6~8):(2~3):(1~3); The preparation of the fermented sludge includes: fermenting the sludge with a compound bacterium agent to obtain the fermented sludge; the compound bacterium agent includes Bacillus stearothermophilus, Aspergillus niger and Trichoderma reesei; The modified bentonite includes citric acid modified bentonite.

2. The soil conditioner according to claim 1, wherein The application forms of the Bacillus stearothermophilus, Aspergillus niger and Trichoderma reesei include bacterium agents, and the mass ratio of the Bacillus stearothermophilus bacterium agent, Aspergillus niger bacterium agent and Trichoderma reesei bacterium agent is (2~4):(1~2):(2~3).

3. The soil conditioner according to claim 1, wherein The fermentation includes aerobic fermentation and anaerobic fermentation carried out in sequence; the temperature of the aerobic fermentation is 50~60°C and the time is 4~8 d; the temperature of the anaerobic fermentation is 30~50°C and the time is 10~20 d.

4. The soil conditioner according to claim 1, characterized in that, The addition amount of the compound bacterium agent is 1%~3% of the dry weight of the sludge.

5. The soil conditioner according to claim 1, wherein The preparation of the citric acid modified bentonite includes: mixing the bentonite and a citric acid solution and then carrying out modification; the mass-volume ratio of the bentonite and the citric acid solution is 1 g:(7~9) mL; the temperature of the modification is 50~90°C and the time is 2~8 h.

6. The preparation method of the soil conditioner according to any one of claims 1 to 5, characterized in that, It includes: Mix the fermented sludge, modified bentonite and lignosulfonate, and then carry out microwave crosslinking to obtain a soil conditioner.

7. The preparation method according to claim 6, characterized in that, The power of the microwave crosslinking is 700~1000 W, and the irradiation time of the microwave crosslinking is 3~5 min.

8. The application of the soil conditioner according to any one of claims 1~5 or the soil conditioner prepared by the preparation method according to claim 6 or 7 in soil improvement.

9. The application according to claim 8, wherein The soil includes saline-alkali soil.

10. The application according to claim 8, wherein The soil improvement includes at least one of the following: 1) Lower the soil pH value; 2) Passivate soil heavy metals; 3) Lower the soil conductivity value; 4) Increase the soil microbial diversity index; 5) Increase the soil organic matter content.

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